It was recently reported that "PAM" cells, a line of transformed mouse cells, show a decreased growth rate, compared to controls, when treated with materials from multiple sclerosis (MS) patients. This decreased growth rate was purportedly the result of a virus-like agent. We have failed to confirm this conclusion. When coded samples were tested in the "PAM" cell assay, significant differences in growth rates were not found for MS and control samples. Titers of antibody to rubella virus in 68 human sera were compared by hemagglutination-inhibition (HI) and enzyme-linked immunosorbent assay (ELISA). In general, the titers measured by ELISA were higher than those found by HI. Although the titers differed, the two methods showed parallel trends. Use of purified rubella virus and addition of 1% bovine serum albumin to the test wash solution aided in reducing false-positive titers in ELISA.